To the arrival of the aging society, the development of orally-disintegrating tablets which can be easily taken by the elderly who have hardness or difficulty in swallowing tablets has been ongoing. With this development, requests for developing orally-disintegrating tablets containing various active ingredients are growing. In case that an active ingredient has a bitter taste, the masking of the bitter taste will be necessary for formulating it into orally-disintegrating tablets and the like. Also, controlled release of an active ingredient may be necessary for increasing the bioavailability of the active ingredient. However, many of the above-mentioned functional particles tend to give some adverse affects to the formulation of tablets (for example, they lack sufficient hardness when homogenously distributed in a tablet), thus it is necessary to add a large amount of additives such as an excipient and a binder to avoid the adverse affects, which make the tablet in an inconvenient big size.
Patent Reference 1 discloses a press-coated rapidly disintegrating tablet as a unique form which has not been well known before. A press-coated tablet has a double-layered structure consisting of the inner core and the outer layer and attracts attentions as a novel technique of formulating tablets. However, the press-coated formulations disclosed in Patent Reference 1 were designed focused on the solubility and degradability of the inner core, and the ingredients of both the inner core and the outer layer comprise ingredients with formability (for example, it appears that the ingredients of the inner core in Patent Reference 1 has formability and a certain hardness, as figured out in the results of Example 2 in which only the ingredients of the inner core were compressed into tablets). Thus, approaches to the application using powder/granular materials with poor formability were not tried, hence Patent Reference 1 disclosed only a limited range of the ingredients of the inner core. Also, the outer layer of the press-coated tablet disclosed in Patent Reference 1 mainly comprises erythritol as a sugar alcohol, and the combination of the essential ingredients of the outer layer of the present invention were not disclosed.
Patent Reference 2 discloses trials applying microcapsule-like granules to the ingredients of the inner core in relation to the formulation in Patent Reference 1 described above. That is, Patent Reference 2 discloses the study to apply microcapsule-like granules to the inner core of the press-coated tablet, and some successful examples of press-coated formulations containing microcapsule-like granules in their inner cores which were prepared using the outer layers comprising lactose and microcrystalline cellulose according to a certain method. However, Patent Reference 2 discloses only the invention of the press-coated tablet containing microcapsule-like granules in its inner core, it does not disclose or suggest any study to apply the press-coated tablets to orally-disintegrating tablets. Additionally, in Patent Reference 2, there was no study about applicable ingredients for the outer layer in the press-coated formulation containing microcapsule-like granules in their inner cores, other than lactose and microcrystalline cellulose. Of course, Patent Reference 2 does not disclose the combination of the essential ingredients of the outer layers of the present invention.
The orally-disintegrating tablet in Patent Reference 3 is characterized in that comprises an active ingredient, microcrystalline cellulose and an inorganic excipient without any disintegrant. Also, as described therein, the orally-disintegrating tablet of Patent Reference 3 has a higher hardness shortly after the compression and more excellent degradability compared with those of orally-disintegrating tablets comprising crospovidone and low substituted hydroxypropylcellulose (for example, Example 5 and comparative Example 5-9). Also, Patent Reference 3 describes that “the present invention without any disintegrant holds a predominant position because disintegrants have side effects that lower the quality of tablets by decreasing the hardness of the tablets, inducing a roughness on the surface of the tablets due to their moisture absorption, and worsening the feeling of the tablets in oral cavity with oral dryness due to their absorption of saliva”. Patent Reference 3 also lacks a disclosure and suggestion related to the press-coated formulations disclosed in the above Patent References 1 and 2.
Patent Reference 4 discloses an orally-disintegrating tablet comprising an inorganic excipient but does not describe a specific disclosure relating to a press-coated formulation.    [Patent Reference 1] WO2003/028706    [Patent Reference 2] WO2005/097041    [Patent Reference 3] WO2005/123040    [Patent Reference 4] WO2007/018192